The present invention relates to a novel type of textile material in sheet form that can be used for technical purposes, such as reinforcing structures for composites, laminated complexes, complexes for sealing in the building field, or in public works, complexes intended for repairing pipes and, more generally, for any type of structure comprising a resin-based matrix, made of polyester or other resin, reinforced by a textile reinforcing sheet.
The use of textile sheets, especially those based on glass fibers, has been proposed for decades for reinforcing a plastic in the manufacture of laminated or molded structures with a plane or shaped, as is apparent, for example, from patents FR-A-1 469 065, FR-A-1 394 271, U.S. Pat. No. 3,930,091, FR-A-2 034 787 and FR-A-2 568 275.
Such textile structures have also been proposed for the purpose of being used in the building field and in public works for the production of impermeable membranes, especially reinforced bitumen membranes (FR 2 409 338) for producing complexes that can be used to repair pipes or similar structures, whether buried or not (EP-A-542 639).
From all these documents, it is apparent that the reinforcing structure must be tailored according to the various applications.
The base structures that have been proposed for decades for producing such reinforcements, especially since the appearance of glass yarns, are, on the one hand, mats which consist of discontinuous fibers and are in the form of a structure similar to a xe2x80x9cfeltxe2x80x9d, and, on the other hand, warp-and-weft fabrics consisting of yarns or roving assemblies based on glass yarns consisting of continuous filaments.
Apart from these types of structure, xe2x80x9cunidirectionalxe2x80x9d sheets have also been proposed in which the glass yarns are arranged in the same longitudinal direction, these yarns being linked together either chemically (French patent 1 394 271) or by means of stitching (French patent 1 469 065).
It has also been proposed in U.S. Pat. No. 3,930,091 to produce a sheet which, unlike the previous ones, consists predominantly of glass fibers extending transversely with respect to the length of said sheet, these yarns being bound together by a binding warp thread, which is loose and consists of yarns coated with a heat-meltable or similar material, making it possible, especially after a heat treatment, to keep the weft yarns parallel to one another.
Compared with balanced warp-and-weft fabrics, such unidirectional sheets do not, however, allow articles reinforced both longitudinally and transversely to be produced.
Moreover, for many applications, the problem arises of how to have a reinforcing structure which can deform upon installing it, especially when articles molded to a shape are produced.
In the case of a reinforcement in the form of a unidirectional sheet, it is possible to obtain such xe2x80x9cdeformabilityxe2x80x9d in the transverse direction with respect to the orientation of the yarns, for example by using elastic yarns as binding yarns.
In the case of a balanced warp-and-weft fabric, it may be envisioned to obtain deformability by selecting the weave.
This is because it is well known that certain weaves, of the satin or twill type, result in deformable woven structures. However, the amount of deformation possible is limited to a few percent.
Such a problem of limited possible deformability of the reinforcement also arises within the context of the use of complex structures consisting of a combination of a nonwoven mat and of bidirectional or unidirectional woven structures, which are used especially for repairing pipes using a technique consisting in covering the internal surface of the structure to be renovated with a tubular structure made from a flexible complex comprising a fluid-impermeable membrane and a fibrous base structure which is impregnated with an uncured synthetic resin and, after said complex has been pressed against the surface of the structure to be repaired, in causing the resin to cure so as to form an internal xe2x80x9csleevingxe2x80x9d.
As regards putting such a tubular structure in place inside the pipe to be renovated, two main techniques have been used hitherto.
The first, which stems more particularly from British patent 1 357 355, consists in introducing the tubular material produced beforehand into the pipe to be renovated in such a way that the fibrous structure is positioned so as to face the surface to be renovated and the impermeable surface layer itself is located on the inside, facing the flow region.
After it has been put into place along the entire length of the pipe, the sleeve is put under pressure so that it is pressed against the internal surface. The resin is then caused to cure.
Another technique, called the xe2x80x9cinside-outxe2x80x9d technique, consists, as is apparent from British patent 1 449 455, in introducing the preformed sleeve with the impermeable surface lying on the outside and then, upon introduction into the pipe, in turning said sleeve inside out so that the fibrous structure comes into contact with the internal surface of the pipe and the impermeable layer lies on the inside.
Such a procedure allows the fibrous structure to be impregnated with uncured resin progressively as it is put into place inside the pipe.
Moreover, the curing may also be carried out continuously, for example by light radiation.
These two techniques, and more particularly the turning-inside-out installation technique, means having a base material which has sufficiently high mechanical properties in the length direction to ensure that it is installed.
Moreover, it is desirable that the tubular structure be able also to be deformable under the action of the stresses exerted in the transverse direction so as to allow the sleeve to rest perfectly against the surface of the wall to be renovated when the structure is pressurized, and to do so so that it follows perfectly the surface of the work to be renovated.
Consequently, in all uses involving textile reinforcements in sheet form, the problem may arise of having the possibility of deformation both in the machine direction and in the cross direction, while maintaining, in the final product (laminated article, molded article, impermeable membrane, complex for pipe repair), high mechanical properties in all directions.
What has now been found, and it is this which forms the subject of the present invention, is a novel type of fabric that can be used either by itself or combined with other structures, such as nonwoven fibrous webs, reinforcing meshes, etc., so as to constitute a complex which not only makes it possible, upon installing it, to retain good mechanical properties, especially tensile strength, both in the warp direction and in the weft direction, while still permitting deformation in the other direction, thereby ensuring in the final product mechanical properties equivalent to those conferred by a nondeformable fabric.
The invention also relates to a process and to a plant for producing such a type of fabric, as well as to the use of the latter to produce complexes such as built-up roofing membranes and pipe-repair structures.
In general, the material according to the invention consists of a warp-and-weft fabric made from twist-free roving assemblies of continuous technical filaments (glass, carbon, aramid, etc.), which roving assemblies will, in the rest of the description, be referred to by the generic term xe2x80x9cyarnsxe2x80x9d. Such a fabric is characterized in that:
the fabric is made in a plain weave or derivative thereof, the density of the warp and the weft preferably being balanced;
the warp yarns or weft yarns are weakened or cut individually at predetermined intervals without any appreciable deterioration in the characteristics of the weft or warp yarns lying beneath the weakening or cutting area; and
the areas in which a series of yarns of the fabric are weakened or cut are produced with a lateral and vertical step between two consecutive yarns or groups of yarns.
In the present description, the expression xe2x80x9ctwo consecutive yarns or groups of yarnsxe2x80x9d is understood to mean that the weakening or cutting carried out is either actually between two yarns with offset of a neighboring yarn or, optionally, in groups of yarns, for example simultaneously on the neighboring yarn, this offset being produced between two consecutive groups.
In the fabric according to the invention, the filament roving assemblies constituting the warp-and-weft yarns are in the form of flattened tapes, of large width compared with the thickness, the width advantageously being between 3 mm and 15 mm, and this being so, both in the warp direction and in the weft direction, whereas the thickness is advantageously between 0.30 mm and 3 mm.
The warp and weft are based on roving assemblies consisting of continuous technical filaments, such as especially glass rovings, the overall linear density of which is between 200 tex and 9600 tex, each consisting of 1 to 8 rovings, having an individual linear density of between 200 and 4800 tex. These rovings are twist-free and the weight of the fabric is in general between 300 g/m2 and 3000 g/m2.
The base fabric is, as indicated above, a fabric produced in a plain weave or derivative thereof. Weaves derived from plain weave, such as gros de Tours, rib, gros de Naples, hopsack or the like, allow the width of the bands of yarns in the warp direction or in the weft direction to be easily varied.
The weakened areas, which will be made either on the warp yarns or the weft yarns, are localized on one side of the material over the entire width of the roving assemblies, the interval between two weakening areas on a given yarn is between 10 and 15 cm. These areas are offset from one yarn to the yarn which is adjacent to it.
Thanks to such a design, a structure is obtained which, despite the weakening, or even the cutting of a series of its constituents (warp yarns or weft yarns), does, however, remain homogeneous and able to be manipulated and possibly allows it to be used as such.
In a preferred embodiment, such a fabric is, before the weakened or cut areas are produced, combined with a fibrous web based on discontinuous fibers, such as a glass mat, the two components being linked together by stitching or knitting, the wales extending in a parallel fashion between the warp yarns, preferably on either side of each yarn, although this is not obligatory.
Optionally, the binding may be obtained by producing not a straight seam of stitches but a true knit of the warp-knitting type, the wales extending along that side of the fabric whose constituents (warp or weft) have to be weakened or cut, and the binding loops on the reverse side of the complex consisting of the fibrous mat.
In such a case, the weakening or cutting of the yarns is preferably carried out between two wales so that the latter are not impaired.
The invention also relates to a process and to a plant allowing such a fabric or complex to be produced.
In general, the process according to the invention consists:
in producing a warp-and-weft fabric from twist-free roving assemblies of continuous technical filaments,
in optionally combining this fabric with a fibrous mat, and is characterized in that a complete or partial cut is made in the warp or weft yarns, at regular intervals, on one side of the fabric, without complete deterioration of the weft or warp yarn in the weakening area beneath the cut yarn, this cut being made with a lateral and vertical step between two consecutive yarns with a lateral and vertical step between two consecutive yarns or groups of yarns which are juxtaposed, working in the same way in the weave of the fabric and to do so in such a way that two consecutive yarns (or groups) can slide one past the other when the material is being used.
Such a process may be carried out in a plant which also forms part of the invention, which plant is characterized in that it comprises, placed between a feed station and a take-up station, an assembly allowing the warp or weft yarns of the fabric to be cut at regular intervals and in a manner offset from one yarn to the neighboring yarn (or group of yarns), said assembly comprising:
two rolls driven in synchronism with the movement of the fabric;
one of the rolls having on its surface a series of blades, the width of which corresponds substantially to the width of the yarns (or groups) to be cut, said blades being offset one with respect to another, both laterally and circumferentially in a pattern reproducing a xe2x80x9csatinxe2x80x9d-type weave.
When it is desired to cut the warp yarns, these blades will be arranged transversely, whereas if it is desired to cut the weft yarns, the blades will be arranged circumferentially.
The second roll is a backup roll coated with a layer of rubber or another elastomer, the pressure between the two rolls being adjustable.
Such a plant allows the action of the cutters to be precisely controlled so that the cutting is carried out only on the warp yarn (or weft yarn) of the visible fabric without the weft or the warp yarn lying beneath the fabric deteriorating.